>> reporter: diane, since the virginia tech shooting, johns hopkins has had an emergency plan in place for a shooting like this. today, we saw it kick into action. s.w.a.t. teams and a hospital on lockdown. for more than two hours, johns hopkins was under siege. >> they moved us all from the front side of the building which faces the hospital to the back. none of us could be by any windows. >> reporter: you had to be scared. >> yeah, it was scary. >> reporter: the standoff began just after 11:00 a.m. outside room 873 of the spinal surgery wing. as dr. david cohen updated 49-year-old warren pardus on his mother jean's operation. >> he became emotionally distraught and reacted. >> reporter: pardus then grew a semiautomatic handgun and shot the doctor once in the abdomen, at close range. >> mr. davis was last seen running into the room, brandishing the handgun in the direction of his mother, who was confined to the bed. >> reporter: at 1:30 p.m., police sent in a camera-equipped robot, which found both pardus and his mother dead, shot in the head. we don't know what the doctor said to him